This invention relates to motor controllers and more particularly, to a delta motor controller that automatically detects when a delta motor system has been wired with permanent single phase connections.
A delta motor system typically includes a delta motor, a three phase power source, a fault contactor and a motor controller. During start up, delta motors often experience potentially damaging high inrush currents and starting torques. This can adversely effect the performance of the motor drive and increase general wear and tear leading to higher maintenance costs. In addition, current peaks during motor startup can also cause voltage disturbances in the power supply.
Motor controllers are typically used to restrict the motor torque and reduce the high starting currents by controlling the application of voltage from the three phase power source to the delta motor. The motor controller generally includes a set of three control switches that are connected between the line voltage terminals of the three phase power source and the windings of the delta motor. The motor controller regulates the voltage from the three phase power source to the delta motor by selectively opening and closing the three control switches. The proper operation of the delta motor is dependent on the proper regulation of the control switches.
The fault contactor is commonly used to disconnect the three phase power source from the delta motor in the event that the delta motor system malfunctions. The fault contactor includes a set of three contacts that are also connected between each of the delta motor windings and the line voltage terminals. Each of the delta motor windings are intended to receive the fault contact connection on one side and the control switch connection on the other side. Alternatively, the fault contactor function can also be done with a shunt trip circuit breaker, an in-line contactor, or fuses.
The motor controller""s internal timing mechanisms are specifically designed to regulate the application of specific line voltages from the three phase power source to specific delta motor windings based on a predesignated wiring configuration. Conventional electrical leads are typically used to connect the delta motor windings to the control switches and to the fault contacts. Since the electrical leads providing connection to the delta motor terminals are not always clearly marked, mistakes in wiring the delta motor system are common.
If the motor winding leads are connected in the wrong positions, such as a permanent single phase connection, then it is possible for current to flow through one of the motor windings. With a permanent single phase connection one of the motor windings is connected between two fault contactor contacts to two of the line terminals. There is no control switch to control supply to the winding. As a result, the winding is permanently connected in single phase as long as the fault contactor contacts are closed. The overload relay operating the fault contactor may not detect this current flow. The motor winding could be damaged.
Clearly it is desirable to use a motor controller that automatically detects a fault condition if the motor system has been incorrectly wired. One example is a single motor winding is wired in a permanent single phase configuration. Detecting this fault condition prior to operating the delta motor enables the user to correct the faulty wiring prior to subjecting the delta motor and the motor controller to potentially damaging current conditions. In addition, automatic detection of these faults reduces troubleshooting time and associated expenses. The present invention seeks to achieve these objectives.
It is a principal object of this invention to provide a new and improved motor controller that automatically detects when a delta motor is wired incorrectly within a motor system. More specifically, it is an object of the invention to provide a motor controller that detects the faulty wiring prior to starting the delta motor so that the incorrect wiring can be corrected and the delta motor and the motor controller are not subjected to potentially damaging current conditions. It is also an object of the invention to facilitate the installation process so that troubleshooting time and associated expenses are reduced.
An exemplary embodiment of the invention achieves the foregoing objects in a motor controller for use in a motor system including a multiphase power source having three supply lines and a delta motor having three windings.
The motor controller includes a plurality of switching means and an error detecting means. Each of the switching means is intended to be operatively connected in series with a selected one of the windings and between an associated selected pair of the supply lines. The error detecting means is operatively connected across each of the switching means to detect a fault condition if at least one of the windings is permanently connected in single phase between a pair of supply lines.
It is a feature of the invention that an indicating means is connected to the error detecting means to generate an indication in response to the fault condition.
In one embodiment, the plurality of switching means comprise solid state devices.
In another embodiment, the plurality of switching means comprise SCRs or triacs.
In another form of the invention, an error detecting means is operatively connected to each of the switching means to detect a fault condition if at least one of first leads for motor windings is operatively connected to one of the supply lines, wherein the winding associated with the at least one of the first leads is permanently connected in single phase between a pair of supply lines.
Other objects and advantages of the invention will become apparent from the following specification taken in conjunction with the accompanying drawings.